Field of the Invention
The invention relates in general to a communication technology, and more particularly to a scheduling method and device.
Description of the Related Art
A Third Generation (3G) mobile communication system usually needs to switch among systems of different standards. Particularly in the next few years, the Second Generation (2G) system having broader coverage, e.g., Global System of Mobile communication (GSM), will coexist with the new 3G system that is targeted at solving high communication volumes in metropolitan areas. This will cause enormous amounts of switching among systems, resulting in larger demands in high frequency switching. The foundation of switching is that, a user equipment (UE) needs to routinely monitor surrounding regions to constantly obtain the power of received signals (a certain Base Transceiver Station (BTS)) and updates of a list of these BTSs from the surrounding GSM BTSs. Further, analog detection of Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) BTSs also need to be simultaneously carried out.
The length of one TD-SCDMA sub-frame is 5 ms, and includes 7 general timeslots and 3 special timeslots. The 7 general timeslots are Ts0˜Ts6, each having a routine timeslot length of 675 μs. More specifically, the 3 special timeslots include a Down Pilot Timeslot (DwPTS) having a length of 75 μs, a Guard Period (GP) having a length of 75 μs, and an Up Pilot Timeslot (UpPTS) having a length of 125 μs. The timeslot Ts0 and the 3 special timeslots may be utilized as broadcasting timeslots used for detecting information of surrounding BTSs.
The length of one GSM frame is 60/13 ms, and includes 8 timeslots each having a length of 15/26 ms. 51 Time Division Multiple Access (TDMA) frames from form one composite frame, 26 composite frames form a super frame, and 2048 super frames form an ultra frame. In the GSM system, the Frequency Correction Channel (FCCH)/Synchronization Channel (SCH) information in composite frames for controlling synchronization occurs in the timeslot Ts0 of the 0th, 10th, 20th, 30th and 40th TDMA frames. The 50th frame at the end is an idle frame, which does not include any information to indicate the end of the composite frame.
FIG. 1 shows a schematic diagram of a conventional TD-SCMDA system scheduling a UE for GSM measurement. To obtain information of the GSM system under the architecture of TD-SCDMA frames, “An Efficient monitoring strategy for intersystem handover from TD-SCDMA to GSM networks” (G. Durastante and A. Zanella, in Proc. Of IEEE PIMRC'02, vol 4, pp. 1555-1560, 2002) provides a measuring method. As shown in FIG. 1, a time interval at a fixed position (the shaded part) is provided in each of the TD-SCDMA sub-frames. The time interval is greater than or equal to 25/26 ms (5/12 ms+the length of one GSM timeslot), and is utilized for searching for the GSM FCCH, so as to ascertain that at least one FCCH falls in the time interval within 660 ms to further guarantee that the FCCH can be identified within 660 ms.
FIG. 2 shows a schematic diagram of searching FCCH/SCH information by adopting the measurement method in FIG. 1. As the length of each TD-SCMDA sub-frame is 5 ms and one GSM TDMA frame is 60/13 ms, the position of the FCCH/SCH information of each GSM TDMA frame relative to the position of one TD-SCDMA sub-frame shifts as time passes. After the length of each GSM TDMA frame, the relative position shifts by (5−60/12)ms=5/13 ms, meaning that one 5 ms TD-SCDMA sub-frame has 13 shift positions. That is to say, the GSM TDMA frame covers the entire 5 ms TD-SCDMA sub-frame after 13 shifts, and cyclically shifts accordingly. Combining the positions where the FCCH/SCH information appears, the FCCH/SCH information occurs once in every 10 TDMA frames of the frames in one GSM composite frame. For example, the 1st FCCH/SCH (TDMA frame 0 in the GSM composite frame) occurs at the position 3 in the TD-SCDMA sub-frames, the 2nd FCCH/SCH (TDMA frame 10 in the GSM composite frame) occurs at the position 3, and so forth. After 13 times, it can be ensured that the FCCH/SCH information of the 0th frame Ts0 of GSM TDMA frames is obtained. Thus, after 660 ms (i.e., 132 consecutive TD-SCDMA sub-frames), it is ascertained that all 13 positions are covered to further guarantee that the FCCH/SCH is successfully identified.
However, for the TD-SCDMA system, in a connection state, the valid time intervals for searching for the GSM FCCH are usually at positions of Ts0, DwPTS, GP and UpPTS. Since the UE needs to perform transceiving of many channels, in addition to performing the FCCH/SCH searching that the GSM measurement requires, the measurement of homogeneous-frequency and heterogeneous-frequency neighboring regions of the TD-SCDMA as well as GSM RSSI measurement also need to be performed during these time intervals. Further, the cycle standards of the above measurement have strict requirements. For example, the TD-SCDMA homogeneous-frequency measurement has a cycle of 200 ms, whereas the TD-SCDMA heterogeneous-frequency measurement has a cycle of 480 ms. Consequently, the above consecutive 660 ms may fail to guarantee a successful FCCH search, indicating that the above measurement is infeasible in actual applications.